Conventionally, liquid crystal display elements, which are made by bonding paired substrates to each other with their electrode-bearing surfaces facing inside and by sealing liquid crystal into the gap between them, have been well known. In such liquid crystal displays, when the distance between the opposing substrates varies due to deformation of the substrates caused by external pressure or other adverse effects, changes in the threshold-voltage value, short circuit in the electrodes between the opposing substrates, disturbance in the orientation of the liquid crystal molecules, etc. tend to occur, thereby making it impossible to provide good display images. For this reason, in order to keep the distance between the paired substrates constant, some methods for placing spacers between the substrates have been suggested; conventionally, either of the following two methods is commonly adopted: (1) a method for spraying spherical particles and (2) a method for forming pillars made of an organic or inorganic material.
Specific examples of the method (1) include a dry method in which spherical fine particles, made of, for example, an organic resin, such as a polymer of divinylbenzenes, are dispersed in a gas flow of nitrogen and then sprayed on the substrates, and a method in which the spherical fine particles are mixed in an alcohol solution or other solutions and sprayed on the substrates in a mist state.
However, method (1) has the following problems: The first problem is that since the fine particles have a coagulating property whereby they coagulate with one another, it is difficult to spray them on the substrates in a uniform manner and consequently to achieve a uniform cell thickness. The second problem is that since it is difficult to control the adherence location of the fine particles, the particles, which have been unintentionally sprayed on pixels, tend to cause defects in the orientation, resulting in low display quality. Further, the third problem is that since the substrates are supported by the spherical fine particles that function as spacers only at their contact points, it is difficult to obtain sufficient strength against external pressure.
Moreover, method (2) more specifically refers to a method in which: an organic or inorganic film is formed with a desired thickness, a resist film is formed thereon, and the resist film is irradiated by ultraviolet lights using a photomask, thereby forming pillars that function as spacers. Here, instead of the resist film, for example, photosensitive organic resins, such as photosensitive polyimide or photosensitive acryl resins, can be adopted.
As described above, advantages of method (2) are that the pillars can be selectively formed on the outside of the pixels, and that the contact surfaces between the substrates and the pillars can be shaped into a desired pattern. Thus, method (2) is superior in the uniformity of the cell thickness, the strength against external pressure, and display quality, as compared with method (1).
Recently, ferroelectric liquid crystal has been taken notice of as a prospective liquid crystal material since it has superior properties, such as having spontaneous polarization and providing high-speed response. However, the disadvantage of ferroelectric liquid crystal is that since it has a structure whose molecule-regularity is closer to that of a crystal, once the molecular orientation has been disturbed, it is difficult to return to its original state, that is, it is susceptible to shock. For this reason, in order to solve the above-mentioned inherent problem with ferroelectric liquid crystal, it is essential to provide a substrate construction that is superior in shock resistance. In order to provide a method for manufacturing such a liquid crystal display element, method (2) is considered to be a more prospective candidate than method (1).
In general, in the conventional manufacturing method (2), after an alignment layer has been formed on an insulating substrate, spacers are formed on the alignment layer. However, the conventional manufacturing methods have the following various problems.
First, the manufacturing process of the spacers may give adverse effects, such as contamination, deterioration, and damage, on the alignment layer. Conventionally, in general, spacers are formed on a substrate that has been subjected to an alignment process, by using a photolithography process wherein photosensitive polyimide, photoresist and other materials are used. Here, solvents, which are used in the photolithography process, tend to give adverse effects on the alignment layer. In this case, since the alignment capability of the alignment layer is lowered, the orientation of liquid crystal molecules becomes ununiform, thereby causing degradation in the display quality.
Moreover, when consideration is given so that spacer materials do not affect the alignment layer, limitations, such as a limitation that spacer materials having a setting temperature higher than the alignment layer can not be used, have to be imposed on the spacer materials.
Furthermore, in the above-mentioned conventional manufacturing method, when the substrates are bonded to each other, the spacers that have been formed on one of the substrates and the alignment layer that has been formed on the opposing substrate are bonded to each other. Here, such a bonding process between the materials of different types raises the following problems: The bonding process is carried out while both of the spacers and the alignment layer are being softened by applying heat under pressure; therefore, when there is a great difference between the respective softening temperatures of the spacers and the alignment layer, the material having the lower softening temperature may not retain its shape upon having a temperature rise to the higher softening temperature. Consequently, for example, if the spacers are deformed, those spacers may enter the pixel portions, thereby causing problems, such as degradation in the display quality and low precision in the cell-thickness control. In contrast, if a sufficient temperature rise is not provided, a sufficient adhesive strength may not be obtained, thereby making the substrates susceptible to deformation under external pressure.